The present invention relates to a semiconductor memory device and more particularly, to a semiconductor integrated circuit pseudo-static random access memory.
The pseudo-static random access memory (RAM) includes a dynamic random access memory cell array which requires refresh operation in the stand-by state, a peripheral circuit for making access to a designated memory cell in the memory cell array and for outputting or inputting data from or into the designated cell, and an internal refresh circuit. It takes advantage of the low cost of a large capacity dynamic random access memory. Its built-in internal refresh circuit accomplishes the refreshing operation for the dynamic random access memory in the stand-by state automatically (self-refreshing mode), eliminating the disadvantage of the dynamic random access memory that requires a complicated external control for refreshment.
The reading or writing operation of the dynamic random access memory matrix should be as fast as possible and accordingly, the memory cycle is made short. For that purpose, a time period from activation or driving of a selected word line to activation or enabling of a sense amplifier is reduced to an extent that the sense amplifier is enabled before 100% of the amount of information (i.e., amount of electric charges) stored in a designated memory cell, which is connected to the driven word line, is transferred to the bit line which is connected to the designated memory cell and to the sense amplifier in case the memory cell stores the "1" information or that the memory cell which stores the "0" information is fully charged. This shortens the data-holding time of memory cells, and therefore, the refreshing period in the self-refreshing mode cannot be made long. It is desirable in view of suppressing the power consumption in the stand-by state to make the refreshing period in the self-refreshing mode 5 to 10 times longer than that in the normal operation. Since the refreshing period cannot be made so long, the power consumption in the self-refreshing operation is increased in the prior art pseudo-static RAM.